The typical compact, mechanical contact type of relay used in the past was a lead relay. A lead relay is furnished with a lead switch, in which two leads composed of a magnetic alloy are contained, along with an inert gas, inside a miniature glass vessel. A coil for an electromagnetic drive is wound around the lead switch, and the two leads are installed within the glass vessel as either contacting or non-contacting. Usually with this type of lead relay, in a non-drive state, current does not flow through the coil, and the ends of the leads repel each other and are not in contact. In the drive state current, current flows through the coil, and the ends of the leads attract each other and make contact.
Lead relays include dry lead relays and wet lead relays. Usually with a dry lead relay, the ends (contacts) of the leads are composed of silver, tungsten, rhodium, or an alloy containing any of these, and the surfaces of the contacts are plated with rhodium, gold, or the like. The contact resistance is high at the contacts of a dry lead relay, and there is also considerable wear at the contacts. Since reliability is diminished if the contact resistance is high at the contacts or if there is considerable wear at the contacts, there have been various attempts to treat the surface of these contacts.
Reliability of the contacts may be enhanced by the use of mercury with a wet lead relay. Specifically, by covering the contact surfaces of the leads with mercury and by using capillary action, the contact resistance at the contacts is decreased and the wear of the contacts is reduced, which results in improved reliability.
In addition, because the switching action of the leads is accompanied by mechanical fatigue due to flexing, the leads may begin to malfunction after some years of use, which also diminishes reliability. Japanese Patent Publication SHO 36-18575 and Japanese Laid-Open Patent Applications SHO 47-21645 and HEI 9-161640 disclose techniques for reducing this mechanical fatigue of the leads, lowering the contact resistance at the contacts, and making the relay more compact overall.
In these publications, the switching mechanism is structured such that a plurality of electrodes are exposed at specific locations along the inner walls of a slender sealed channel that is electrically insulating. This channel is filled with a small volume of an electrically conductive liquid to form a short liquid column. When two electrodes are to be electrically closed, the liquid column is moved to a location where it is simultaneously in contact with both electrodes. When the two electrodes are to be opened, the liquid column is moved to a location where it is not in contact with both electrodes at the same time.
To move the liquid column, Japanese Laid-Open Patent Application SHO 47-21645 discloses creating a pressure differential across the liquid column. The pressure differential is created by varying the volume of a gas compartment located on either side of the liquid column, such as with a diaphragm. Japanese Patent Publication SHO 36-18575 and Japanese Laid-Open Patent Application HEI 9-161640 disclose creating a pressure differential across the liquid column by providing the gas compartment with a heater. The heater heats the gas in the gas compartment located on one side of the liquid column.
The technology disclosed in Japanese Laid-Open Patent Application 9-161640 (relating to a microrelay element) can also be applied to an integrated circuit. Also, as the technology continues to develop, this type of relay may be made even more compact and faster, as disclosed by J. Simon, et al. (A Liquid-Filled Microrelay with a Moving Mercury Drop, Journal of Microelectromechanical Systems, Vol. 6, No. 3, September 1997). Furthermore, this type of relay may no longer be gravity dependent (attitude dependent), the mercury contacts may have a much longer service life, reliability may be enhanced, and even environmental pollution during manufacturing may be kept to a minimum.
FIG. 1 is a plan view of the layout of the latch-type thermodrive microrelay elements disclosed in Japanese Laid-Open Patent Application HEI 9-161640. The microrelay elements are formed in a specific region of a semiconductor substrate 91 and include an active reservoir 921, a passive reservoir 922, and a channel 93. The active reservoir 921 and passive reservoir 922 are each provided with a plurality of cantilevered heaters 941 and 942, and the active reservoir 921 and passive reservoir 922 are connected by the channel 93. In FIG. 1, a heater support stand is provided under the heaters 941 and 942.
A microchannel region 931, having a smaller diameter than the channel 93, is formed at a location midway along the channel 93. A first channel region 932 is formed on the active reservoir 921 side of the microchannel region 931, while a second channel region 933 is formed on the passive reservoir 922 side. The first channel region 932 is connected to the active reservoir 921 via a first narrow channel 934, and the second channel region 933 is connected to the passive reservoir 922 via a second narrow channel 935. First signal electrodes 951 and 952 are exposed in the first channel region 932, and second signal electrodes 954 and 955 are exposed in the second channel region 933. The channel portion consisting of the microchannel region 931, the first channel region 932, and the second channel region 933 is filled with a liquid metal 96, which serves as a conductive fluid column.
With the microrelay in FIG. 1, the first signal electrodes 951 and 952 can be "opened" and the second signal electrodes 954 and 955 can be "closed" by heating the heater 941 to raise the internal pressure of the active reservoir 921. This internal pressure rise of the active reservoir 921 causes the liquid metal 96 to move to the second channel region 933. Similarly, the first signal electrodes 951 and 952 can be "closed" and the second signal electrodes 954 and 955 can be "opened" by heating the heater 942 to raise the internal pressure of the passive reservoir 922. This internal pressure rise of the passive reservoir 922 causes the liquid metal 96 to move to the first channel region 932.
With a conventional microrelay as shown in FIG. 1, the relay is "closed" by moving a column of conductive fluid so that the fluid is simultaneously in contact with two electrode components. The relay is "opened" by moving the column so that it is not in contact with the two electrode components at the same time. The electrical switching point corresponds to the contact between the conductive fluid and the electrode components of the solid electrodes.
With a microrelay element having a structure as shown in FIG. 1, there is the danger that the surfaces of the electrodes will become rough or that the electrode surfaces will be corroded by components of the gas inside the channel 93 in the course of switching the first signal electrodes 951 and 952 or the second signal electrodes 954 and 955. As a result, the switching action may be unstable and reliability may diminish.